Messages in this thread | | | Date | Tue, 23 Jul 2002 16:56:48 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [patch] irqlock patch -G3. [was Re: odd memory corruption in 2.5.27?] |
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On Wed, 24 Jul 2002, Ingo Molnar wrote: > > - slab.c needs to spin_unlock_no_resched(), instead of spin_unlock(). (It > also has to check for preemption in the right spot.) This should fix > the memory corruption.
That cannot be right.
If we want to drop a spinlock but remain non-preemptible, we should comment that a _lot_, and not just say "xxxx_no_resched()".
In fact, I personally think that every "spin_unlock_no_resched()" is an outright BUG. Either the spin_unlock() makes us preemptible (in which case it doesn't matter from a correctness point whether we schedule immediately, or whether something else like a vmalloc fault might force us to schedule soon afterwards), or the spin_unlock is doing something magical, and we depend on the preemptability to not change.
In the latter case (which should be very very rare indeed), we should just use
/* BIG comment about what we're doing. */ /* We're dropping the spinlock, but we remain non-preemptable */ __raw_spin_unlock(..);
and then later on, when preemptability is over, we do
local_irq_enable(); preempt_enable();
so that we _clearly_ mark out the region where we must not re-schedule.
It is simply not acceptable to just play games with disabling interrupts, and magically "knowing" that we're not preemptable without making that clear some way.
Please get rid of spin_unlock_no_schedule() and friends, ok?
Linus
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